Seminarium "Teoria cząstek elementarnych i kosmologia"

After a brief review on tachyon fields and their role in Cosmology–Inflation, we introduce the inflationary scenario based on the tachyon field coupled with and without the radion of the second Randall-Sundrum model (RSII). The tachyon Lagrangian is derived from the dynamics of a 3-brane moving in the 4+1 dimensional bulk, i.e. with one extra dimension. Varying the free parameters and initial conditions we confront our numerical results with the Planck 2015 and Planck 2018 data. We also consider the RSII model extended to more general warp functions, i.e. with a self-interacting scalar field. It leads to modification of the scale dependent four-dimensional gravitational constant. Further, we present a study of the cosmological particle creation in the RSII model extended to include matter in the bulk. The presence of matter modifies the warp factor. We conclude with the same setup proposed in the framework of holographic cosmology. This consideration is based on a holographic braneworld scenario with a D3-brane located at the holographic boundary of an asymptotic ADS5 bulk. The tachyon field that drives inflation is represented by a DBI action on the brane. The parameters of the inflation are calculated in the slow-roll regime.